> What about ZeroMQ and if one also needs to temporarily store the queued data at least until it's delivered? ZeroMQ is blazing fast, damn simple and battlefie

> What about ZeroMQ and if one also needs to temporarily store the queued data at least until it's delivered? ZeroMQ is blazing fast, damn simple and battlefield proven. However it is also pretty low level. Things like ACL, topic filtering or user management often need to be reimplemented on top of it. That is not the case for most MQTT blockers. Also if security is a a big concern for you, I would pick up MQTT+HAProxy+TLS anytime over an ZMQ with CurveMQ and its home-made security.